This proposed research has two long-range objectives. First, it seeks an understanding of the interactions among the excited states leading to efficient intersystem-crossing in carbonyl compounds. These studies will elucidate the fundamental photophysical processes resulting in lethal or mutagenic lesions induced in DNA by UV-light and ionizing radiations. Such radiation damages are conducive to the formation of skin cancer. Secondly it acquires knowledge of the intramolecular non-radiative processes which quench the lowest triplet state, resulting in little or no phosphorescence. These knowledge are invaluable in attempting to eliminate energy wastage in photochemistry. We employ the method of optical detection of magnetic resonance, both at zero field and in high field. With the help of the resonant microwaves we will study the populating and decay kinetics of the individual spin-levels of carbonyls and alpha-dicarbonyls in the triplet state. The techniques of microwave-induced delayed phosphorescence and microwave saturation recovery will be employed. We will determine the precise triplet state geometry of carbonyls with the high-field ENDOR technique. An innovative attempt will be made to observe proton ENDOR in zero-field.